This invention relates to additive compositions, also known as admixtures, for incorporation in hydraulic cement mixes, for example, hydraulic cement concretes, mortars, grouts, neat cement mixes, nonplastic cement or concrete mixes, such as concrete block mixes, and dry mixes for making such concretes, mortars, and grouts.
Admixtures are employed to achieve, among other things, water reduction, improved compressive strength, and radiation of the rate of hardening and setting of cement mixes. Frequently, greater compressive strengths are obtained when reduced quantities of water are utilized in hydraulic cement mixes, and so often water reduction and increased compressive strength are achieved together. As retarders, such admixtures slow the chemical process of hydration so that the concrete remains plastic and workable for a longer time than concrete without such a retarder. Among the materials commonly used for water reduction and improved compressive strength, which also act as set retarders, are the lignosulfonates, such as calcium lignosulfonate; salts of hydroxycarboxylic acids; sugars such as glucose (dextrose), maltose, sucrose, fructose, and the like; and highly polymerized polysaccharides, such as dextrins.
Admixtures having set retarding properties are useful as set retarders per se, for example, to delay the set of the cement during difficult placements that require the concrete to be in a plastic condition for a longer than normal period of time or to overcome undesired acceleration of set during hot weather. If the set retarders also achieve improved compressive strength then the improved compressive strength is a supplemental benefit.
Also, additives or admixtures are frequently used in combinations to achieve certain results or overcome inefficiencies, such as where an admixture does not produce a sufficient or significant improvement in the compressive strength or does not effect the desired or a significant degree of retardation while producing other necessary and/or desirable effects. To overcome or assist or amplify these undesirable or insufficient effects, such as for example, an excessive amount of retardation, well known accelerators, such as calcium chloride and triethanolamine, that increase the rate of hydration for early strength development are frequently used. Thus, admixtures which can be used in combination with other admixtures are also desirable.
It is known in the art that some, although not all, plant derived products and carbohydrates will beneficiate concrete or mortar when employed as small percentage additions to the plastic mixes. Some of these, such as molasses, derived from sugar cane or sugar beets, also fall into the category of simple sugars. For example, U.S. Pat. No. 2,311,290 discloses the use of blackstrap molasses in an amount in the range of 0.01% to 0.1% based upon the weight of the concrete. U.S. Pat. No. 3,432,316 also discloses a useful admixture for cement and concrete mixes, which is based upon the use of plant derived products, namely a portion of the tobacco plant, such as aqueous extracts and comminuted cured tobacco plant. This discovery resulted in an admixture which produces a beneficial increase in the compressive strength of the hardened cement mix.
Further materials known to the art for improving the strength of concrete and mortar are the highly polymerized polysaccharides, such as the dextrins. The polysaccharides are less severe retarders of cement hydration than the simple sugars, and they can be used without danger of complete or severe inhibition of hydration and hardening.
U.S. Pat. No. 3,432,317 discloses the use of saccharide polymers, composed of glucose units having a size range of from three to on the order of twenty-five glucose units, as additives for cement mixes. The glucosaccharides are disclosed as being more advantageous than more highly polymerized polysaccharides and more highly depolymerized products. While such an admixture as U.S. Pat. No. 3,432,317 may perform adequately as a means for increasing compressive strength in cements, concretes and mortars, the potential unavailability of materials for producing such admixtures makes alternative admixtures, which produce corresponding desired effects, desirable and necessary.
The problem of unavailability would apply to other known additives and admixtures. Increasing demands can make admixtures unavailable. Lignosulfonates, for example, are not as ubiquitously available as they once were due to the pressures of, among others, environmental restrictions which have forced suppliers to find means of consuming these materials through their own corporate channels. Also, sugars and dextrins are subject to the whims and fancies of speculative interests, and so have become quite costly, as well as occasionally being unavailable.
Further, the increasing cost and unavailability of energy has made it desirable to find, in addition to alternative additives and/or admixtures per se, additives and admixtures which require only a minimum or reduced amount of energy to produce.
Thus, a need exists for new, alternative additive or admixture compositions for incorporation in hydraulic cement mixes, which additives will provide improved compressive strength for or control of the rate of hardening of the resulting cement products, while not causing adverse effects in the hydraulic mixes.